Diffusion-reaction characteristics of benzene hydrogenation utilizing a supported nickel catalyst

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Virginia Polytechnic Institute and State University

An experimental investigation of the characteristics of benzene hydrogenation over nickel/kieselguhr catalyst has been made in a differential bed reactor. The study was performed at moderate temperatures (340 to 474 K), and atmospheric pressure. A Langmuir-Hinshelwood rate model assuming the Rideal-Eley mechanism for addition of molecular hydrogen to adsorbed benzene was used to describe the data. From kinetic rate data the parameters of the model were found (reproducing the experimental data to within ±10.9%).

Diluting the reactant stream with nitrogen (an inert), while maintaining total pressure, temperature, and benzene mole fraction constant, linearly decreased the observed reaction rate.

The diffusion-reaction characteristics of this fluid-solid system were observed by increasing the particle size, thereby forcing intraphase transport limitations to occur. Experimental effectiveness factors were compared to theoretical ones generated using the dusty gas model. Minimizing the residual sum of squares between the two yielded relationships for the effective diffusivity and the catalyst tortuosity, both of which reproduced values reported in the literature. These relationships were based on Knudsen diffusivity being the controlling diffusive mechanism, a fact shown to be true for the catalyst used in this study.